1. Field of the Invention
The disclosed invention generally relates to fire simulation by emittance of radiation that simulates one or more distinguishing attributes of the radiant energy produced by a fire, and more particularly, is directed to fire simulation apparatus and methods for simulation of substantially all of the key attributes of a fire which distinguish it from other sources of radiation.
2. Description of the Technology
Fire simulators are used to check the operation of optical fire sensor systems which are in use in a variety of military and civil applications. The military, for example, deploys a number of such fire sensor systems in fighting vehicles to trigger fire-quenching Halon gas should the vehicle's crew compartment be subjected to an incipient fire from an armor piercing shell. Such systems are important in protecting the lives of vehicle occupants. Engine compartments in vehicles are also protected from fire by optical fire sensor systems. Aircraft "dry" bays, that is compartments not containing fuel, are protected by fire sensor systems which warn the crew of fire and may dispense fire-quenching material. Such sensing systems have many potential uses for protecting persons and equipment in closed areas from ignition and fire.
Fire simulating systems are used to test the operation in the field of installed fire sensor systems as well as operation on the test bench or at the factory. Checks of fire sensor systems for proper operation precedent to use under actual conditions must of course use simulated fire stimuli in most circumstances. Open flames cannot be used generally as a test source since flammables are often present. Fire sensors are designed to avoid response to non-fire stimuli, so it is not surprising that known simulators are narrowly designed to include only the principal fire-like stimuli upon which a particular sensor to be tested operates.
To test a fire sensor requires presenting it with one or more distinguishing features of a fire. The main distinguishing features of a fire are smoke, noise, light and heat. Fast-responding optical fire sensor systems respond to a fire's light and heat radiation. This radiation may roughly be divided into a region of ultraviolet and visible light, and infrared radiation.
In particular, the main distinguishing attributes of the radiant energy emitted by a glowing fire have been found by investigators to be: light and heat represented by 1200 degrees to 1700 degrees Kelvin blackbody radiation from about 0.4 to 25 micrometers wavelength; carbon dioxide and water vapor spectral radiation emission in bands mainly at about 2.7 and 4.3 micrometers wavelength; ultraviolet light from about 0.20 to 0.32 micrometers wavelength; and a flickering pattern, which is a change of emitted radiation varying in time. It has been found that the energy emitted is nearly constant for flickering frequencies of 0 to 5 Hertz and then rolls off roughly as the inverse of the flickering frequency.
A fire which glows yellow, such as burning wood for example, emits radiation having a characteristic blackbody shape, and the heat energy tends to dominate the light emissions. A natural gas fire which glows blue, also has characteristic blackbody radiation but the ultraviolet, CO.sub.2 and H.sub.2 O emissions tend to dominate the heat energy. Burning of different materials could be simulated by adjusting the relative amplitudes of radiation from manufactured sources of radiant energy which generate the light, heat and spectral emissions indicative of a fire.
Known optical fire sensor systems sense one or at the most two of the distinguishing features of a fire in order to perform detection. As a result, known fire simulators have catered specifically to individual fire sensor system technologies. While these simulators are satisfactory for the sensor systems they are designed to test, such systems, because they simulate only one or perhaps two key characteristics, are useful only to test a sensor system that operates on those particular characteristics.
A proliferation of various fire sensor system technologies has produced a need for a "universal" fire simulator which will test all of the currently deployed designs as well as systems with new technologies which are still not constructed or even conceived. Military services in particular, that have a variety of systems installed in aircraft and ground vehicles, could save time and expense by procuring one universal fire simulator with which to test and maintain all of their deployed systems.
The use of a universal fire simulator obviates the need to use an actual fire to test fire sensing systems even where possible, for example, in laboratory or field test-stand evaluation. Improved safety, cleanliness and dependability would result from the use of such a simulator.
A universal fire simulator would be especially useful if it were small enough to be held in the palm of one's hand, particularly while testing aircraft or vehicle-installed fire sensors. Frequently, fire sensors are installed in crowded compartments with only minimal access through hand-access holes.
A universal fire simulator which closely simulates a fire is useful in testing fire sensors which are particularly subject to environments which may produce false alarms. Such a system would have the ability to simulate all of the key distinguishing attributes of a fire so the features of a fire sensor system which prevent false alarms are exercised. Protecting against false alarms is of prime concern in most fire sensor systems. When automatic dispensing of fire quenching or retardant materials is included in the application, false alarms can be disastrous because of the possible damage to equipment from such materials. Inappropriate fire alarms which prompt action by aircraft or vehicle crew members are likewise not desirable.
None of the known fire simulating systems closely simulate all of the main distinguishing features of a fire or an ignition and fire, nor do they provide a basis for reducing the size of such simulating systems to a size that is usable in the restricted space and access of aircraft or vehicle compartments. Critical fire sensor systems, therefore, might not now be tested fully while installed.
A practical and reliable means for closely simulating all of the key attributes of a fire, particularly in a small, portable size, would constitute a major advancement in the art of fire simulation. Users of fire sensor systems could employ such a system to test more fully and verify the operation of a variety of fire sensor systems in the field, on the test stand or on the production line. It is likely that they could do so at reduced costs and with improved results over currently known fire simulating systems. The aim of the present invention is to help accomplish this major advancement in the art.